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Mendel's First Law

Each trait is controlled by particular factors that occur in pairs. These pairs separate during gamete formation so that each gamete receives one pair of diploid chromosomes. The double number is restored upon fertilization.

Test Cross

Crossing to a pure breeding recessive organism

Gene

One of Mendel's "factors" that controlled the traits that he observed.

Allele

An alternate form of a gene (ie yellow and red)

Gamete

Sex cell, sperm and egg, or ovum and pollen.

Gametes carry only 1/2 the regular number of chromosomes. This number is restored upon fertilization.

Zygote

Formed by the fusion of two gametes.

Homozygote

A cell that carries identical alleles of a gene (ie AA)

Heterzygote

A cell that does not carry identical alleles of a gene.

Mendel's Second Law

Law of independent assortment:

Genes for different traits assort independently of one another. In other words, genes on different chromosomes behave independently in the production of gametes.

How can you tell if two alleles are alleles of the same gene?

They separate during gamete formation.

When you see distorted Mendelian ratios, what should you expect?

two or more genes are involved in determining the phenotype.

Epistasis

Masking the effect of one gene by the allele of another gene.

Pleiotrophy

what is the disease associated with this word?

pleiotrophy is the production of superficially (phenotypically) unreleated effects by a single allele.

It was impossible to get a pure breeding line of yellow rats because the YY genotype was lethal and the rats died in utero. This means that y is an essential gene, without this allele the rat dies.

Penetrance

The percentage of carriers that are affected in the same way.

expressivity

The degree to which phenotype is altered in those that are affected.

probability

Proportion of time an even is expected to occur in repeated trials.

binomial formula

P= n!/((s!)(t!)) (p)to the s times (q) to the t

What is the cut off for the P value which says that our data does not fit the model well enough to keep it?

5%

what is chi squared?

(observed - expected )squared all over expected.

August Weismann

he did experiments to see if physical changes were incorporated into our genetic material and passed on to the next generations. He cut off the tails of 22 generations of mice to see if the trait would become heritable. It did not.

Interphase

-phase between cell divisions
- chromosomes are elongated and difficult to see under light microscope
-stain cell --> see chromatin

Prophase-

condensation occurs until separate bodies called chromosomes are distinguishable.
-centrioles slowly move to opposite poles.
-spindle proteins slowly form
-nuclear envelope completely breaks down by the end of prophase

Metaphase

Spindle fibers line the chromosomes up on the metaphase plate .

-microtubules attach at the kinetochore, or region near the centromere of the homolog

Anaphase

Movement of chromosomes to opposite ends of the cell.

what is a daughter chromosome?

the name for each of the sister chromatids once they have separated and begun to migrate towards opposite poles.

Telophase

-daughter chromosomes assemble at the opposite end and elongate.
-nuclear envelope reforms and the spindle breaks down.
-nucleolus reforms.

by looking at chromosomes we discovered?

1. chromosomes occur in morphologically identical pairs

2. chromosome types are constant within a species and form a karyotype

Describe prophase I of Meiosis I

the cell forms a temporary 2n stage, when the homologs double and there are 2 centromeres. the sister homologs associate and a bivalent is formed. This is where crossing over occurs.

chiasm

the place where crossing over takes place.

How are the products of meiosis II different from the products of mitosis

- Mitosis produces a cell that has the same number of chromosomes as it started out with.

-There is not crossing over in mitosis

-meiosis creates 4 haploid gametes which are NOT identical to the original diploid cell because crossing over has allowed the genetic material to recombine and enhance gametic diversity.

What did elanor carothers do?

observed that a mutant strain of grasshoppers had a short variation of one chromosome

-she observed and accessory chromosome that assorted independently of the short variant of chromosome.

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